Bird detection is needed in order to effectively take measures against collision between a bird and an airplane or the like, what is called a bird strike. For example, detecting a bird in an airport makes it possible to take countermeasures such as repelling birds with a blank shot sound and preventive measures such as identifying birds' range of activities to remove their feeding ground.
Regarding detection of birds, PTL 1 discloses a flying object detection system for detecting an object flying from the windward side of a wind generator device which includes: a tower erected on the ground, a nacelle fixed to the tower, and a plurality of blades rotatably fixed to the nacelle through a hub.
The flying object detection system includes: image capturing means which is provided behind the blades in the nacelle and limits an image capturing region to the windward side; image capturing control means which controls to allow the image capturing means to capture image at a timing when turning blades do not obstruct the image capturing region; data processing means which processes data to make the data suitable for detecting a flying object by using the captured image data obtained by the image capturing means; detection means which detects a flying object based on the data processed by the data processing means; and detection result output means which outputs a detection result provided by the detection means to the wind generator device.
PTL 1 states that the flying object detection system efficiently reduces bird strikes in a wind generator device.
PTL 2 discloses a bird threatening device which includes: an image capturing device which continuously takes captured images of a predetermined spatial region; a bird detection device which uses the optical flow method to calculate the speed of a flying object in an image based on a mode change among a plurality of pieces of image data taken by the image capturing device and determines that the flying object is a bird if the calculated speed of the flying object is equal to or greater than a predetermined speed and reasonably corresponds to a bird's speed; and a threatening device which outputs a threatening output toward a predetermined spatial region when the bird detection device detects a bird.
PTL 2 states that the bird threatening device increases the probability of avoiding bird strikes by calculating the speed of a flying object in real time, determining that the flying object is a bird, and effectively threatening birds, without using a high-performance computer.
PTL 3 describes using the particle image velocimetry or the optical flow method for a bird detection algorithm for detecting birds.
More specifically, according to PTL 3, when the particle image velocimetry is used, birds are regarded as particles and are detected on the basis of how the particles are moving in images taken by an imaging unit.
According to PTL 3, when the optical flow method is used, a bird is detected by calculating the velocity vector at the individual position coordinates in an image taken by the imaging unit and determining that the velocity vector is attributable to a bird if the velocity vector in terms of size or direction exceeds a predetermined reference value.